After Robin van Persie joined Manchester United in 2012 and helped carry the club to its 19th and last league title (to date), Arsene Wenger was so stung by the implication that he may have gift-wrapped a championship to his longtime rival, Sir Alex Ferguson, he vowed never to sell another player to United again.

That lasted six years.

On Monday, Arsenal, once again, sent its talisman to Old Trafford as Alexis Sanchez officially joined in a rare player-for-player trade for Henrikh Mkhitaryan. The deal, reportedly, will involve no transfer fee, meaning United was able to land a world-class talent and proven Premier League goal scorer for a player that was languishing on the bench.

Much like the van Persie deal, the Sanchez transfer had once seemed unlikely - even unthinkable. After all, the ex-Barcelona ace had seemed intent on a reunion with Pep Guardiola at Manchester City, going so far as to try and force through a move to the Etihad over the summer. The move didn’t happen then, but it seemed inevitable that Sanchez would join the blue part of Manchester one way or another. His contract was expiring, so City could wait and snap him up on a Bosman in July. Or Sanchez could try and force through a move in January, which is what most observers assumed would happen as the winter transfer window opened.

However, a few complications arose. First of all, given City’s outstanding form, to say nothing of its 12-point lead, it’s debatable whether Pep even needs Sanchez. Bringing in a star of Sanchez’s magnitude could hurt team chemistry and force one of the team’s bright attacking stars to the bench. Additionally, City went back on UEFA's financial fair play radar after its summer spending spree, so maybe the brass decided that there was no need to call even more attention to itself.

Then, United decided to jump into the sweepstakes. Whether Ed Woodward and Jose Mourinho were driven by a genuine interest in signing Sanchez or they were simply trying to drive up his value while unsettling two of its rivals is something only they know. Either way, it worked as Sanchez’s agent reportedly upped his financial demands - a move that may have angered Guardiola and other City officials enough for them to walk away from the bargaining table.

The deal also seemed unlikely given the managers involved. If Wenger and Ferguson didn't exactly get along, they were best friends compared to Wenger and Jose Mourinho. Yet, the two (via their football directors) have made deals before. Mourinho let both Lassana Diarra and Petr Cech join Arsenal, and most notably, in 2006, both managers signed off on a swap deal that had Ashley Cole join Chelsea with William Gallas going to Arsenal.

As a result, United has its first world class, league-proven #7 since Cristiano Ronaldo. While it's fair to wonder just how Sanchez will fit into the team's attack (and whether he's the Gunner that Mourinho really needs - or wants), it's indisputable that this team desperately needs an unpredictable player like him that can create goals out of nothing and strike fear at the hearts of defenders. This club struggles to score against organized teams that sit back and defend and adding someone like Sanchez could give them a weapon that they haven't really had since that first season with van Persie (although Zlatan was able to steal goals for them from time-to-time last season). This is one of the great coups in recent Premiership history and one that could deliver the league title next season (assuming this year’s race is already over).

And things could, ultimately, work out for Arsenal. With Mkhitaryan going the other way, Wenger has a pretty good building block for the future (especially if Mikhi’s old Dortmund teammate, Pierre-Emerick Aubameyang, joins as rumored). Mkhitaryan is a phenomenally talented player who, for whatever reason, never quite fit with Mourinho’s plans. If Wenger can figure out how to get the best out of him, then he could make United regret selling him for years to come.

Indeed, the Cole-Gallas swap provides an interesting parallel. In both cases, you had an Arsenal star getting his head turned by the promise of big money and silverware. Additionally, you had a talented, albeit temperamental player going to the Gunners. Like Gallas, Mkhitaryan is a player that needs to be nurtured and protected and Wenger might be the guy to succeed where Mourinho and Jürgen Klopp were unable to. It stinks to let a talent like that walk (especially one that was desperate to play for United and seemed to genuinely love being at the club), but that's buisness.

Either way, it looks like this move should help both teams. Manchester United gets its man and Arsenal makes the best of a bad situation. See what happens when you take personal feelings out of business, Arsene?